Loading-and burning-proof electromagnetic coil

ABSTRACT

A loading- and burning-proof electromagnetic coil used, for example, as rotor and stator windings in which coil of high resistive wire is allowed to cohere with a cohering mixture of an epoxy resin having a molecular weight of above 800 and a curing agent therefor other than acid anhydride type curing agent.

United States Patent Imai et al.

[ 51 Oct. 10, 1972 [63] Continuation-in-part of Ser. No. 783,762, Dec.

13, 1968, abandoned.

[52] US. Cl. ..336/205, 117/218, 117/232 [51] Int. Cl. ..HOlf 27/30 [58] Field of Search.336/205; 174/1 10.43; 260/47 P;

[56] References Cited UNITED STATES PATENTS 2,856,547 10/1958 Saums ..336/205 X 3,355,427 11/1967 Loncrini .,l74/l 10 X 451,872 5/1891 La Boiteaux ..310/261 UX 2,822,483 2/1958 De Jean ..310/45 X 2,837,669 6/1958 Fisher ..310/45 OTHER PUBLICATIONS Skeist, 1., Epoxy Resins, Reinhold, N.Y., 1962, (pp 40, 41 & 285) lmidazoles, Houndry Prod. C0., Data Bulletin, Philadelphia, Pa., 4-1959, (pp 1, 2 & 6)

Birks, J. 8., Modern Dialectric Materials, Heywood & Co., 1960, London, (pp 136 & 137) Primary ExaminerJ. D. Miller Assistant Examiner-R. Skudy Attorney-Cushman, Darby & Cushman [5 7] ABSTRACT A loadingand burning-proof electromagnetic coil used, for example, as rotor and stator windings in which coil of high resistive wire is allowed to cohere with a cohering mixture of an epoxy resin having a molecular weight of above 800 and a curing agent therefor other than acid anhydride type curing agent.

5 Claims, 3 Drawing Figures PATENTEDum 10 I972 8.697.913

FIG.

INVENTORS T4 KES/V/ fM/9 ATTORNEYS LOADING-AND BURNING-PROOF ELECTROMAGNETIC COIL CROSS-REFERENCES TO RELATED APPLICATIONS This is a continuation-in-part of copending application Ser. No. 783,762 filed on Dec. 13, 1968, now abandoned.

The present invention relates to an improved electromagnetic coil, and particularly to a loadingand burning-proof electromagnetic coil such as rotor, stator windings and the like which are used in electric machinery in a car or an electrodriving tool.

The said loading is a mechanical load of the centrifugal force and vibrating shock. The recent tendency is towards accelerating the speed of car, making machinery mounted thereon small and using under severe conditions electrodriving tool as well as making it small and light. This is requiring an electromagnetic coil resistive 'to loading due to the centrifugal force and vibrating shock and also to burning during the locked running.

Responding to the above requirements, excellent heat-resistive wires have been developed, and an excellent burning-proof electromagnetic coil has been produced as far as it is limited to that formed by the insulated wire alone. However, the problem of making the coil loading-proof or burning-proof in combination with loading resistance is not still resolved.

it has been attained, heretofore, by impregnating the above mentioned electromagnetic coil with a solvent type varnish as a cohesive agent for adhering the wire mutually to render the coil loading-proof. Among such a cohesive agent, a specific heat-resistant varnish, for example, amideimide varnish is sold, but the varnish is inferior in loading-resistance despite of its high superiority in buming-resistance. In addition, there is a considerable drawback in the cohering agent which causes a poor workable performance due to necessitating dripping off the varnish and taking much time to dry up the solvent and to cure under heating. Accordingly, a trail is recently directed to give the coil the loading-resistance by impregnating it with a liquid mixture of liquid epoxy resin which is known as a sort of non-solvent type varnish and a curing agent therefor. Thus, an excellent loading-resistance of the coil may be obtained by appropriate selection of the curing agent to be added to such a non-solvent type varnish as the epoxy resin for accelerating the curing time. However, there are some drawbacks in the use of the above non-solvent type varnish, which drawbacks are the facts that the more accelerated the curing is, the shorter the shelf life of the varnish becomes, and further the handling of the varnish is troublesome. Besides, the most important drawback has been found in case of the use of a heatresistive wire impregnated with the non-solvent type varnish for the purpose of improvement of bumingproof in such a way that when, for instance, the coil is heated at elevated temperature resulting from electroconducting under locked conditions, the burning and short circuit of the coil occur below the softening temperature of the insulation coatings on the electric wire used, resulting in the use of such heat-resistive wire in vain, while there are no such problems in case of the use of low heat-resistive wire.

Therefore, an object of the present invention is to provide an improved, strongly cohered, insulated electromagnetic coil having an excellent loadingand buming-proof in combination.

Another object of the present invention is to provide the above electromagnetic coil in high workable performance.

The inventors sturdied precisely the above facts causing the drawbacks of the non-solvent varnish cohered coil and have found that the mixture of nonsolvent type varnish such as liquid epoxy resin and the curing agent is dry-distilled at an elevated temperature, even after the mixture is cured by heating, and this results in the formation of a lower molecular tar which causes the insulation coatings on the wire to swell, peel off and short-circuit at a temperature lower than the softening point of the insulating coatings. In such study, it has been found that the wire used is such one that the temperature of occurrence of short-circuit between the conductors is not less than 300 C when the insulated wire is crossed at right angle to each other, and heated at a rate of 2 to 3 C per minute while supplying AC. voltage of volts to the insulated wire under a load of 200 grams at the cross point.

The above facts were also, confirmed in that when the wire coated with heat-resistive insulating material was dipped in a liquid monomeric epoxy resin and heated in this state the coatings swelled at a temperature lower than their softening point by 100 to C. From the phenomenon, it will be appreciated that the dry-distilled tar previously mentioned contains the same component as the liquid monomeric epoxy resin, and the component renders the insulating coatings swelling and peeling off.

As well known, a common liquid epoxy resin has, in general, a relatively low average molecular weight such as less than 700, and usually below 400. The present inventors effected the above test using an epoxy resin having an average molecular weight not less than 800, and found facts that such swelling and peeling off did not occur at a temperature lower than the softening point of the coating even in case of the heat-resistively coated insulating wire. It goes without saying that it was confirmed that no burning and short-circuit were also observed in an electromagnetic coil whose wire is mutually cohered with a mixture of an epoxy resin having an average molecular weight not less than 800 and a curing agent. However, when an acid anhydride typecuring agent was used in this case the burning and short-circuit were observed even by the use of the epoxy resin having an average molecular weight not less than 800.

Thus, such type of curing agent should be excluded in the present invention, and the curing agents used in the present invention are amine type such as diamino diphenyl methane, meta-phenylene diamine, diamino diphenyl sulfone, etc.; amide type such as dicyandiamide, etc.; and acid type such as BF -mono-ethylamine, etc.

The application of such epoxy resin having an average molecular weight of not less than 800 and containing added thereto the above mentioned curing agent as a coherent agent for insulating wires, imparts not only burning-proof and the prevention of line-toline short-circuit to the cohered electromagnetic coil,

3 but naturally also a loading-proof property equivalent or superior to that in the application of the liquid epoxy resin containing a curing agent therefor.

Accordingly, one of the feature of the present invention rests on a loading-proof and strongly wire-cohered electromagnetic coil having also buring-proof properties equivalent or superior to that of a specifically used heat-resistively insulated wire per se, which is prepared by making a coil of insulated wire which has coatings of any one of the insulating material such as polyester, polyesterimide, polyamideimide, polyirnidazolone, polyimide, or modified material thereof in either monolayeror multilayer structure, and has a temperature of short-circuit between the conductors of above 300 C when crossed at right angle to each other and heated at a rate of 2 to 3 C per minute while supplying AC. voltage of 100 volts to the insulated wire under a load of 200 grams at the cross point; allowing the coil wire to cohere with a mixture comprising as main component an epoxy resin having an average molecular weight of above 800 and a curing agent therefor other than acid anhydride type. Preferably the average molecular weight of the epoxy resin is from 800 to 3,800.

In addition, it was found that a cohering mixture having fast curable and easily handling properties as well as prolonged shelf life is produced in the combination of the relatively high molecular epoxy resin mentioned before and an imidazole type fast-curing agent that is a solid at room temperature and has been recognized unsuitable for curing a liquid epoxy resin. The use of such a cohering agent was achieved from the consideration that both components are solid. By the use of imidazole type curing agent, the epoxy resin reveals further remarkable effects as mentioned above.

The example of such imidazole type fast-curing agent is, for example, represented by the formula wherein R R and R are same or different and signify hydrogen atoms, alkyl groups having one to 12 carbon atoms. This includes 2-methylimidazole, 2-undecylimidazole, 2-ethyl-4-methyl-imidazole and l-butylimidazole and the like.

The second feature of the present invention rests on, therefore, an electromagnetic coil having not only the same favorable properties as in the aforementioned electromagnetic coil but also higher working performance, which is made by applying the cohering mixture comprising the epoxy resin having a molecular weight not less than 800 and the imidazole type curing agent to the electric coil made of heat-resistively coated wire.

The production of the electromagnetic coil according to the present invention will be more precisely explained. At first, the coil is formed into desired form as a substrate used by winding up the insulated wire coated with the insulating material such as polyester, polyesterimide, polyamideimide, polyimidazole polyimide or modified material thereof in the form of monolayer-structure, or with the insulating materials in combination to form a multilayer structure, the insulated wire having a temperature of short-circuit between conductors of above 300 C when crossed at right angle to each other and heated at a rate of 2 to 3 C per minute while supplying A.C. voltage of volts thereto under a load of 200 grams at the cross point. On the other hand, the cohering mixture is prepared by mixing an appropriate amount of the curing agent other than acid anhydride type with the epoxy resin having a molecular weight of above 800, and pulverizing the mixture to an appropriate particle size. Subsequently, the coil is preheated and attached with the resulting powder by means of the fluidized-bed dipping method or spray method, and optionally heating the coil to cure the mixture and cohere the wound wire thereof. Thus, the loadingand buming-proof electromagnetic coil according to present invention is obtained.

The process for producing the electromagnetic coil suitable for higher working performance according to the feature of the present invention is carried out in the same way as described above, with exception that the cohering mixture is prepared by mixing the epoxy resin having a molecular weight of above 800 which has been pulverized to an appropriate particle size with the solid imidazole type curing agent capable of pulverization such as Z-methylirnidazole, Z-undecyI-imidazole and the others which has been also pulverized to an ap propriate particle size, melting and kneading the mixture to such an extent as not to effect the curing reaction, cooling the melted mixture and pulverizing to the desired particle size for application.

In the attached drawings:

FIG. 1 generally represents a rotor having a coil of the present invention,

FIG. 2 is a cross-sectional view of the rotor of FIG. 1, and

FIG. 3 is an enlarged view of a portion of rotor of FIG. 1, in which 1 refers to a rotating shaft, 2 refers to an armature core, 3 refers to an insulating coating on the core, 4 refers to an insulated wire, 4 refers to a conductor, 5 refers to an insulating coating on the conductor, 6 refers to a commutator, and 7 refers to a wire cohering agent.

The following examples illustrate the present invention, but it will be appreciated that the present invention is not limited thereto.

Table 1 shows the loadingand buming-proof properties as well as performance of electromagnetic coils according to the present invention as well as those to the conventional technique as comparison. The electromagnetic coils are made as rotor windings of a 12 volt wiper motor equipped in a car, and they are a coil having an insulating wire of 0.6 mm in diameter wound by 28 turns on a rotor core with 12 slots and a specific varnish thereon.

Table 2 shows the same which are made as rotor windings of a 12 volt washer motor for equipping in a car, and they are a coil having an insulating wire of 0.22

mm in diameter wound by 55 turns on a rotor core with 5 slots and a specific varnish thereon.

It will be appreciated in Tables 1 and 2, that in both of the examples of the present invention and comparative examples the insulating wire and the cohering composition are specifically shown.

The method for cohering the wound wire is not explained in detail. In Examples 1, 2 and 3 in Table l as well as Examples 5, 6, 7 and 8, each of the electromagnetic coils was prepared as follows:

One hundred Parts by weight of an epoxy resin having an average molecular weight of 1,400 (registered trade name: Epikote 1004 (a diglysidyl ether of bisphenol A having a QB. viscosity C) of A-U, a melting point of 95 105 C, an epoxy equivalent of 870l,025 and a hydroxy equivalent of 175) sold by Shell Chemical Co.) were added with 17 parts by weight of diamino-diphenyl methane (referred to as DDM), the mixture was melted with kneading and pulverized into a powder having a particle size of 80 mesh after cooling. The coil each prepared as above mentioned was heated to 160 C, dipped into the fluidized bed of powder of the resulting cohering mixture to be coated and impregnated therewith, and then cured in a furnace at a temperature of 180 C for minutes. In Example 4 in Table 1 and Example 9 in Table 2, a cohering mixture was prepared bymixing 100 parts by weight of the epoxy resin same as above (Epikote 1004) previously coarse-pulverized in a particle size suitable for mixing with 1 part by weight of 2- methylimidazole (referred to as 2M1) which had been also pulverized in the same way, melting the mixture under kneading to such an extent as not to cause a cure reaction, cooling and then pulverizing into a powder having a particle size of 80 mesh. Then, the electromagnetic coils in both Tables were produced, respectively, by dipping the coil each prepared as above into the fluidized bed of powder of the cohering TABLE 1 and a curing agent therefor, which is known as having a superior loading-proof property among the non-solvent type varnish is used in the other Comparative Examples. Furthermore, in Comparative Examples 5 and 10, there are shown a coil without treatment with varnish.

The electromagnetic coils thus prepared were tested for loading and buming-proof properties. The measure of loading-proof property is indicated as a rotation rate and time required to cause the break down of a wire when subjecting the coil to centrifugal force. That of buming-proof property is indicated as time required to cause the burning, as cycle for burning and as temperature of core at burning, when subjecting the coil to continuous lock test with conducting to wire by applying a voltage of DC. 14.5 under continuous lock in case of the wiper motor of Table l, and to interrnitted lock test with the same voltage but under the intermitting lock consisting of a cycle of the application for 10 seconds and the shutting of for 5 seconds in case of the washer motor of Table 2. The measure of performance is indicated as the heat-curing condition and the shelf life of the used cohering mixture in both tables.

Loading-proof (centrifugal test) r.p.m. (min.)

Insulated wire used Cohering mixture Example N 0.:

Polyester-insulated Epikote 1004 DDM. 25,00 (5) O.K.

2 Polyamideimide-insulated do Polyimidazolone-insulated .do

4 Polyamideimide-insulated. Epikote 1004 2M1 Comparative Exainple' Polyamidaimide-insulated- Polyimidazolone-insulated- Polyamrdeimide-insulated 5 do Polyester-insulated Epikote 8282' 25,

Burning-proof Working performance Shelf-life of curing mixture Time required (min.)

Core temp. at burning,

C. Curing condition 180 C.for6min Shours 180 C.for6min Do. 375 180 01016111111..." D0. 200 C.f0r 2hrs 3months. 40

Trade name of a curing agent, modified aromatic amine.

TABLE 2 Insulated wire used Cohering mixture Loading-proof (centrifugal test) r.p.m. (min.)

- Burning-proof Working performance Time required (min) She1f-life of curing mixture Core temp.

at burning, C.

Curing condition Example No.:

5 Polyester-insulated.

Polyamideimide-insulate 7 Polyester-polyimide-insulated in two-layer structure.

9 Polyamideimidc-insulated Comparative Example:

0 Polyester-insulated 7. 8 lolyester-polyimide-insulated in two-layer structure.

Epikote 1004 2M1- 10 lolyaniidcimide-insulated 2-ethyl-4-methy1 imidazole.

Epikote 1004 DDM 30,000 5) 0.x-

do 30,000 a) 0K 8 Polyimide-insulated .do 30,000

Epikote 828 EMI 30,000 (5) OK... Polyamideimlde-insulated .do 30,000 (6) 0K... ..d0 30,000 (5) O.K.

0 Polyiinide insulated .do 30,000 (5) O .K...

N one 28,000 moving 180 C. for 30 min- 180 C. for 30 min- 180 C. for 30 min.

180 C. for 30 min- 180 C. for 2 min Do. Do.

Do. Do.

180 C. for 4 min 7 hours. 276 0 180 C.for4min C.for4min Do.

460 180 C. for 4 min- 465 of upper.

3 months.

As clearly shown in the above tables, it will be understood that the electromagnetic coils of Examples 1, 2, 3, 5, 6, 7 and 8 according to the present invention are remarkably superior to those of Comparative Examples 1, 2, 3, 6, 7, 8 and 9 in the burning-proof property, but almost same in the loading-proof property, as compared therewith. It will be appreciated that those of Examples 4 and 9 are remarkably superior not only in performance but also in loadingand burningproof properties.

In the examples, there are used an epoxy resin having an average molecular weight of 1,400, but it goes without saying that such a characteristic according to the present invention can be also obtained by the use of any epoxy resin having that of above 800. Nevertheless, the use of an average molecular weight of above 3,800 renders the impregnation of the cohering mixture into the coil difficult, and is considered unsuitable for cohering the inner parts of coil. However, the exclusion of the use of such high molecular weight resin is, of

course, not intended in the present invention, since the characteristics of the present invention can be revealed by the use of a mixture of such resin in a minor amount such as at most 30 parts by weight per 100 parts by weight of the resulting cohering mixture with the epoxy resin having a molecular weight of below 800. Furthermore, diaminodiphenylmethane is used in all of the Examples, but the use of any curing agents other than acid anhydride type can give the characteristics same as above to the electromagnetic coil. However, it is preferable to select such a curing agent that the amount required to cure the cohering mixture is not more than 30 parts in the mixture. Otherwise, the resulting electromagnetic coil shows a tendency to somewhat inferior burning-proof property.

In addition, the cohering mixture may contain fillers or pigments in such an amount as not to disturb the coherence to the coil wire.

There is used in the examples of Table 2 only 2- methylimidazole which is pulverizable at ordinary temperature in combination with the solid epoxy resin, as an example of the cohering mixture suitable for high performance. However, there can be used other solid imidazole type curing agents capable of pulverization either at ordinary temperature as they are, or in any conditions as they are made, and the characteristics shown in examples are revealed therewith. Thus, a fastcurable imidazole curing agent which lacks pulverizability at ordinary temperature, such as 2-ethyl-4- methylimidazole, l-butylimidazole and the like can be pulverized by the procedure, for example, of mixing a minor amount of a solid epoxy resin for a filler therewith, or cooling to such a temperature as to make it pulverizable, and the feature of the present invention can be also revealed by the use of such curing agent. The use of the curing agent is favorable as it is easily available.

Therefore, it is contemplated in the specification and claims that the words solid imidazole type curing agent capable of pulverization mean an imidazole type curing agent which is pulverizable in the state of solid by using any procedures to use it as solid state. In any event, it is important that the curing agent is in the state of pulverizable solid, since the powder of curing agent facilitates the uniform dispersion of the curing agent in the solid epoxy resin used.

As disclosed herein, it will be appreciated that in accordance with the present invention such an effect that strongly wire-cohered electromagnetic coil having a burning-proof property equivalent or superior to that of the insulating wire per se can be obtained in the first instance, by making a coil of an insulating wire which has a temperature of short-circuit between the conductors of above 300 C when crossed at right angle to each other and heated at a rate of 2 to 3 C per minute while supplying A.C. voltage of volts to the wire under a load of 200 grams at the cross point, and allowing the coil wire to cohere with a mixture comprising an epoxy resin having a molecular weig t of 00 as a main component and a curing agent there or ot er than acid anhydride type curing agent, thereby allowing the wire to cohere without burning at a temperature of below the softening point of the insulating coatings of the wire.

In addition, another effect can be obtained in the second instance according to the present invention, which effect is to provide an electromagnetic coil having the same properties and, in addition, higher working performance and lower cost, accordingly, resulting from the use of a pulverized cohering mixture comprising the same epoxy resin and solid imidazole type curing agent capable of pulverization as a fast curable and prolonged shelf-life curing agent.

What is claimed is:

l. A loadingand burning-proof electromagnetic coil comprising an insulated wire having coatings of an insulating material selected from the group consisting of polyesters, polyesterimides, polyimideamides, polyimidazolones and polyimides in the form of at least one layer of these different insulating materials and having a temperature of short-circuit between conductors of above 300 C. when crossed at right angle to each other and heated at a rate of 2 to 3 C. per minute while supplying A.C. voltage of 100 volts thereto under a load of 200 grams at the cross point, said coil being cohered with a pulverized mixture comprising, as the main component, a bisphenol type epoxy resin having an average molecular weight of about 800 and a solid curing agent therefor capable of pulverization selected from the group consisting of amine type curing agents, amide type curing agents, acid type curing agents and tidazols time. HY ESFBE 2. A loadingand burning-proof electromagnetic coil according to claim 1, wherein the mixture comprises,

verized mixture comprising as .main component a bisphenol type epoxy resin having an average molecular weight of 800 to 3,800 and a solid imidazole type curing agent capable of pulverization and having a fast curable property.

4. A loadingand burning-proof electromagnetic coil according to claim 3, wherein said insulated wire has coatings of an insulating material selected from the group consisting of polyesters, polyesterimides, polyimideamides, polyimidazolones and polyimides in UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. 3,697,913 Dated October 10, 1972 Takeshi IMAI; Tamotsu MA'ISUBARA; Osamu TAKENAKA Inventor(s) It is' certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN TI-IE READING Item [73], change Osamo Takenaka to O samu TAKENAKA Add: I

[30] Foreign Application Priority Date April 9, 1968 Japamp....,...235M9/68 Signedend sealed this 17th day of April 1973.

(SEAL)- Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,697,913 -Dated October 10, 1972 Takeshi IMAI; Tamotsu MA'ISUBARA; Osamu TAKENAKA Inventor(s) It is' certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE READING Item [73], change Osamo Take'naka to Osamu TAKENAKA Add: 7 [30] Foreign ApplicationPriority Data April 9, 1968 I Japan.. 35 9/ Signed-and sealed this 17th day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM P's-1050 (10-69) I I usqoMM-Dc loan-P61 u K GOVE NENY 'Illifl'lfls; OFFICE 1!. 0-36-33 

2. A loading- and burning-proof electromagnetic coil according to claim 1, wherein the mixture comprises, as the main component, a diglycidyl ether of bisphenol A having an average molecular weight of 1,400 and diaminodiphenylmethane.
 3. A loading- and burning-proof electromagnetic coil comprising an insulated wire having a temperature of short-circuit between conductors of above 300* C when crossed at right angle to each other and heated at a rate of 2* to 3* C per minute while supplying A.C. voltage of 100 volts thereto under a load of 200 grams at the cross point, said coil being cohered with a pulverized mixture comprising as main component a bisphenol type epoxy resin having an average molecular weight of 800 to 3,800 and a solid imidazole type curing agent capable of pulverization and having a fast curable property.
 4. A loading- and burning-proof electromagnetic coil according to claim 3, wherein said insulated wire has coatings of an insulating material selected from the group consisting of polyesters, polyesterimides, polyimideamides, polyimidazolones and polyimides in the form of at least one layer of these different insulating materials.
 5. A loading- and burning-proof electromagnetic coil according to claim 3, wherein the pulverized mixture comprising as main component a diglycidyl ether of bisphenol A having an average molecular weight of 1400 and 2-methylimidazole. 